ATHENS — Greek anarchists vandalized the Athens home of the United States ambassador with black paint on Wednesday, according to the police, in the latest protest against the authorities’ rejection of a convicted terrorist’s request for a furlough.

The vandals defaced Ambassador Geoffrey R. Pyatt’s home about 4 a.m. before fleeing on motorcycles, a police official said. Eight people were briefly detained for questioning before being released without charge because of a lack of evidence linking them to the vandalism.

It was the second attack this year on Mr. Pyatt’s residence: In January, the home was vandalized to protest the United States’ support for Greece’s deal to recognize Macedonia on the condition it changed its name to North Macedonia. Anarchists defaced the embassy in the same month, protesting “American imperialism.”

In a post on Twitter, Mr. Pyatt, who was nominated by President Barack Obama to the post in 2016, described the Wednesday attack as “childish vandalism,” adding that he would “continue to work with Greek authorities to punish the culprits according to the law.” He added, “Destruction of property is not peaceful protest.”

The Greek Foreign Ministry also condemned the attack as an “unacceptable and irresponsible action, which nonetheless shall not affect the friendship and the expanding cooperation between our two countries.”

An anarchist group called Rouvikonas claimed responsibility for the attack in a video posted on social media. It said it had acted in solidarity with Dimitris Koufodinas, an imprisoned hit man for the now-defunct November 17 domestic terrorist group, which killed 23 people, including a C.I.A. station chief in Athens, a British military attaché and several Greek businessmen. He is serving 11 life sentences for his role in the group, which was active from 1975 to 2002.

Mr. Koufodinas, 61, who has never expressed regret for his actions, has been granted six furloughs in less than two years, much to the chagrin of the relatives of the victims of November 17 and foreign missions that had been targeted by the organization.

He began a hunger strike on May 2 to protest a decision by a Greek judicial council to turn down his latest request for prison leave. He was hospitalized as a precaution at the end of last week.

Last summer, Mr. Koufodinas was transferred from the capital’s high-security Korydallos Prison to an agricultural prison in Volos in central Greece as part of an overhaul of the Greek penitentiary system. That move fueled widespread criticism, with many accusing the leftist government of showing lenience to a convicted terrorist.

“Prisoners’ furloughs are a right won through blood, not a concession or a privilege,” Rouvikonas said in a statement. “The pressures from the American Embassy and the domestic political rabble will not pass. Furlough the hunger striker Dimitris Koufodinas now.”

The Greek administration has also been criticized for not cracking down on the activities of anarchists who for years have targeted government buildings, diplomatic missions and businesses to express anti-establishment views, usually through acts of vandalism that do not cause injury.

Wednesday morning’s attack was the latest in a string of acts expressing solidarity with Mr. Koufodinas. It came a few hours after a firebomb attack on a riot police unit in central Athens that followed a march for Mr. Koufodinas.

On Tuesday, 15 assailants wielding firebombs and gas canister bombs attacked a police precinct in an eastern Athens suburb and left a police guard with minor head injuries. Earlier that day, arsonists targeted the car of a Greek crime reporter, apparently because of her coverage of a surge in attacks by anarchists.

Last week, anarchists went on a vandalism spree in central Athens, smashing storefronts and shouting slogans in support of Mr. Koufodinas.

Police chiefs held an emergency meeting this week to come up with a plan for dealing with a possible escalation in violence by anarchists if Mr. Koufodinas continues his hunger strike and his health deteriorates.

Police guards, meantime, say they have had enough. In a statement on Tuesday, their union said that officers’ lives were being put at risk and that the authorities were taking a soft line toward Mr. Koufodinas and his supporters.

“The state and the judiciary are being crudely blackmailed,” the union said.